1. Field of the Invention
The present invention relates to an ink jet recording head which discharges ink to perform recording and an ink jet recording apparatus which is equipped with the ink jet recording head.
2. Related Background Art
The ink jet recording apparatus equipped with the ink jet recording head is configured to record an image on a recording medium (material onto which the recording is performed) such as paper, plastic, or an OHP (Overhead Projector) sheet based on supplied recording information. As used herein, the term of “image” shall include not only images, such as characters, symbols, and graphics, which have individual meanings but also images, such as patterns and solid coloring, which do not have the meanings. The terms of “recording” and “image formation” shall mean the whole of the image forming operation.
In the configuration of the ink jet recording apparatus, the ink supplied to the ink jet recording head is discharged toward the recording medium such as recording paper by heating or vibration, and thereby the image is recorded on the recording medium. An ink droplet which is discharged from the ink jet recording head and deposited on the recording medium spreads on the recording medium to form a dot. The image which is of an aggregation of the dots is formed on the recording medium. An area of one dot depends largely on a size of the ink droplet, i.e., an ink discharge amount. Therefore, in order to form the fine image by the ink jet method, it is necessary to control the ink discharge amount.
The ink discharge amount depends largely on an ink temperature and a recording head temperature, and the discharge amount is increased or decreased according to a fluctuation in temperature. Therefore, it is necessary to manage the temperatures of the ink jet recording head and the ink. Particularly, in a low-temperature environment, viscous resistance is increased in an ink discharge nozzle (hereinafter referred to as “nozzle”) of the ink jet recording head with increasing ink viscosity, which significantly decreases the ink discharge amount.
Therefore, Japanese Patent Laid-Open No. H07-52387 discloses a configuration in which a temperature-retention heat generating element (hereinafter referred to as “temperature control heater” or “sub-heater”) is provided in the ink jet recording head. In the ink jet recording head disclosed in Japanese Patent Laid-Open No. H7-52387, in the low-temperature environment, the sub-heater is driven to increase the temperatures of the ink jet recording head and the ink, and stabilization of the ink discharge amount is achieved.
Recently, in tendency of the ink jet recording apparatus, the ink droplet discharged from the ink jet recording head is finely formed as much as possible in order to realize high-quality recording equivalent to a photograph. Therefore, there is another problem that enhanced speed of high-quality recording is required.
In order to achieve both the high-quality image and the high-speed printing, there is known a technology in which the image is formed by combining dots having different droplet sizes (different liquid amounts). This enables the-dots having different diameters to be arranged in the image, and the image can be formed by the relatively small droplets in a portion where granularity is low. Further, this method enables the wide area to be efficiently filled with the smaller number of ink droplets using the relatively large ink droplets. Therefore, high-speed and high-quality image can be formed.
In the ink jet recording head which discharges the fine ink droplet, because an aperture area of the ink discharge port at a front end of the nozzle tends to be decreased to increase the viscous resistance of the nozzle, when the temperature falls, there is a fear that the decrease in ink discharge amount occurs in a short time in order to perform the temperature-retention control at high response to stabilize the ink discharge amount, it is effective that many sub-heaters, are installed. However, in this method, a substrate area where the sub-heaters are provided is enlarged. As a result, the problem of production cost increase is generated while upsizing of the whole of the ink jet recording head is caused.